<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script type="text/javascript">
			// 页面加载完了之后出发onload事件
			var num1Obj;
			var num2Obj;
			window.onload = function() {
				num1Obj = document.getElementById('num1Id');
				num2Obj = document.getElementById('num2Id');
			}
			
			// var num1 = document.getElementById('num1Id').value;
			// var num2 = document.getElementById('num2Id').value;
			  // 把变化的部分作为参数传递过来
			  function cal(type) {
				  var num1 = num1Obj.value;
				  var num2 = num2Obj.value;
				  var result = eval(num1 + type + num2);// '3+5'
				  /* var result = 0;
				  switch(type) {
					  case '+':
						result = parseInt(num1)  + parseInt(num2);
					  break;
					  case '-':
						result = parseInt(num1)  - parseInt(num2);
					  break;
					  case '*':
						result = parseInt(num1)  * parseInt(num2);
					  break;
					  case '/':
						result = parseInt(num1)  / parseInt(num2);
					  break;
					  default:
					  break;
				  } */
				  var resultObj = document.getElementById('resultId');
				  resultObj.value = result;
			  }
			  
			  
			   function add() {
				   // 重构
				   //var inputObj = document.getElementById('num1Id');
				   //var value = inputObj.value;
				   var num1 = document.getElementById('num1Id').value;
				   var num2 = document.getElementById('num2Id').value;
				   var result = parseInt(num1) + parseInt(num2);
				   var resultObj = document.getElementById('resultId');
				   resultObj.value = result;
			   }
			   
			   function sub() {
				   var num1 = document.getElementById('num1Id').value;
				   var num2 = document.getElementById('num2Id').value;
				   var result = parseInt(num1) - parseInt(num2);
				   var resultObj = document.getElementById('resultId');
				   resultObj.value = result;
			   }
			   
			   function mul() {
				   var num1 = document.getElementById('num1Id').value;
				   var num2 = document.getElementById('num2Id').value;
				   var result = parseInt(num1) * parseInt(num2);
				   var resultObj = document.getElementById('resultId');
				   resultObj.value = result;
			   }
			   
			   function div() {
				   var num1 = document.getElementById('num1Id').value;
				   var num2 = document.getElementById('num2Id').value;
				   var result = parseInt(num1) / parseInt(num2);
				   var resultObj = document.getElementById('resultId');
				   resultObj.value = result;
			   }
		  </script>
	</head>
	<body>
		<table>
			  <tr>
				 <td><img src="" /></td>
				 <td colSpan="3">购物简易计算器</td>
			  </tr>
			  <tr>
				 <td>第一个数</td>
				 <td colSpan="3">
					 <input type="text" id="num1Id" />
				 </td>
			  </tr>
			  <tr>
				 <td>第二个数</td>
				 <td colSpan="3">
					 <input type="text" id="num2Id" />
				 </td>
			  </tr>
			  <tr>
				 <td>
					  <input type="button" value=" + " onclick="cal('+')"/>
				 </td>
				 <td>
					 <input type="button" value=" - " onclick="cal('-')"/>
				 </td>
				 <td>
					 <input type="button" value=" * " onclick="mul()"/>
				 </td>
				 <td>
					 <input type="button" value=" / " onclick="div()"/>
				 </td>
			  </tr>
			  <tr>
				 <td>计算结果</td>
				 <td colSpan="3">
					 <input  type="text" id="resultId" />
				 </td>
			  </tr>
		  </table>
		  
	</body>
</html>
